In a known system of the general type described above, for example that described in U.S. Pat. No. 2,826,998, the two pivoted linkages are disposed above and below the passageway and the lower of the two pivoted linkages includes a lightly domed bridge plate which is pivotable around a transverse axis disposed at the face end of the carriage box. Other bridge members, on which the bridge plate lies in scale-like manner, are supported on the threshold of the portal frame either directly or by means of a support system which is itself supported by the railway coupling lying below, as is the portal frame. A disadvantage of this construction is that the coupling must cooperate in the function of the passageway system and is thus loaded by the portal halves. This type of construction makes the use of non-loadable couplings impossible. Furthermore, the known construction cannot accommodate substantial differences in height as between the two carriage frames which may take place if one of the two railway cars experiences a spring breakage.
Further known is a passageway system as described in U.S. Pat. No. 1,012,451, in which each of the portal halves is supported from below by a coupling carrier and from above by a pivoted linkage connected in the region of the carriage roof. This pivoted linkage includes a telescoping device which may be pivoted around a vertical axis mounted at the carriage but at some distance from the end face of the carriage box and located in the interior of the carriage box. In the region lying somewhat outside of the plane defining the end face of the carriage box, the spring-tensed telescoping device has mounted to it a lever arm which pivots around a vertical axis, the other end of the lever arm being fastened to a vestibule frame of the associated vestibule half. In this disposition, the vestibule half is carried by one of the coupler carriers and thus shares in the lateral motion of the coupler. The bridge which the passengers use in their passage from one car to the other includes a rigid plate extending from the end face of the carriage box on which lies a bridge plate that can glide on the rigid plate in the manner of a fish scale and which is mounted movably around a transverse axis at the threshold of the vestibule frame.